Cambridge Spies papers: Elizabeth II was left in the dark over traitor Anthony Blunt, declassified files show

Queen Elizabeth II was left in the dark for almost a decade over the full scale of the treachery of Sir Anthony Blunt – one of her most senior courtiers – according to newly-declassified files.

Blunt, the surveyor of the Queen’s pictures and a distinguished art historian, confessed in 1964 that he had been a Soviet agent since the 1930s having been recruited while at the University of Cambridge into one of the 20th century’s most notorious spy rings.

During the Second World War Blunt, a senior MI5 officer, passed vast quantities of secret intelligence to his KGB handlers but was allowed to maintain his position at the heart of the British establishment amid fears of a scandal if he was sacked and the truth became public.

When the Queen was finally told the full story in the 1970s, she was characteristically unflappable – taking it “all very calmly and without surprise” – according to MI5 files released to the National Archives in Kew.

The decision to ensure the Queen was fully informed came amid concern in Whitehall that the truth would inevitably come out when Blunt, seriously ill with cancer, died and journalists would no longer be restrained by concerns of libel.

In February 1973, Prime Minister Edward Heath ordered preparations to be put in place for dealing with an expected torrent of negative publicity, including instructions to Sir Martin Charteris, the Queen’s private secretary, to inform the monarch.

On March 19, MI5 director general Michael Hanley reported that the cabinet secretary Sir Burke Trend had shown him a “personal manuscript letter” from Sir Martin confirming she had finally been told.

Mr Hanley noted: “Charteris wrote that he had spoken to the Queen about the Blunt case. She took it all very calmly and without surprise.”

According to the official history of MI5 by Professor Christopher Andrew, Mr Heath was later informed the Queen had not been entirely in the dark as she had been told “in more general terms about a decade earlier”.

However, she apparently did not mention any earlier briefing, acknowledging she was aware of suspicions about Blunt when his fellow spies, Guy Burgess and Donald Maclean, fled to Russia in 1951.

“Obviously somebody mentioned something to her in the early 1950s, perhaps quite soon after her accession,” Mr Hanley wrote.

Four months earlier, in November 1972, Mr Hanley had met Sir Martin to urge Buckingham Palace to sever its links with Blunt. But Sir Martin refused, saying there was little point as Blunt’s position was drawing to a close.

“Charteris thought the Queen did not know and he saw no advantage in telling her about it now; it would only add to her worries and there was nothing that could done about him,” Mr Hanley reported.

“Contrary to what Blunt may have said in the past, Charteris affirmed that the Queen was not at all keen on Blunt and saw him rarely.”

The files suggest contacts between MI5 and the palace over Blunt had been sporadic.

In April 1964, the then director general, Sir Roger Hollis, briefed Sir Martin’s predecessor, Sir Michael Adeane, just as they were about to confront Blunt with new evidence of his treachery which finally led to his confession.

“Sir Michael Adeane thanked me for letting him know the position,” Sir Roger reported. “He said that he did not propose to tell anyone else about it, but asked that we should let him know if there later appeared any possibility of publicity so that he could at that stage take the necessary action.”

Sir Michael was apparently not briefed again until October 1967, more than three years after Blunt owned up, and then only because of the “risk of publicity” due to a Sunday Times investigation into another Cambridge spy, Kim Philby.

Miranda Carter, who wrote a 2001 biography of Blunt, said she believed the Queen would have been told informally some time after 1965.

“It’s the job of a private secretary to a monarch to inform them and protect them. It seems to me she probably needed to know about Blunt in order to know how to behave if she came into contact with him,” she said.

The Queen’s apparent ignorance of events was matched by that of Sir Alec Douglas-Home, her then Prime Minister, who also was not informed of Blunt’s admission.

In an extraordinary misjudgment for which he later apologised, home secretary Henry Brooke, who was in in the know, chose not to tell Douglas-Home because he did not want to “add to his burdens”.

The files suggest MI5 was deeply reluctant to share information about the case with anyone in government – as late as July 1965 Sir Burke had still not been informed, nor had any ministers in the new Labour government which had taken office the previous October.

Blunt was finally unmasked by Prime Minister Margaret Thatcher in a Commons statement in 1979. Stripped of his knighthood, Blunt died in 1983, aged 75.

The files are being released ahead of a major new exhibition focusing on the work of MI5 being staged at the National Archives.

Exhibits will include a vivid report of Blunt’s interview when he finally owned up after MI5 officer Arthur Martin confronted him with testimony from Michael Straight, a young American Blunt had recruited to work for the Russians in the 1930s.

“He sat and looked at me for fully a minute without speaking. I said his silence had already told me what I wanted to know. Would he now get the whole thing off his chest,” Mr Martin wrote.

“Blunt’s answer was, ‘Give me five minutes while I wrestle with my conscience’. He went out of the room, got himself a drink, came back and stood at the tall window looking out over Portman Square.

“I gave him several minutes of silence and then appealed to him again to get it off his chest. He came back to his chair and told me this story.”